Cutting tool

ABSTRACT

A cutting tool includes a portion made of a high hardness material. The portion includes a rake face, a flank face, and a cutting edge. The rake face is divided into a region A along the cutting edge and a region B excluding the region A of the rake face, a surface roughness of the region A is smaller than a surface roughness of the region B, and the region B is deepened with respect to a position of the region A.

TECHNICAL FIELD

The present invention relates to a cutting tool that includes a portioninvolved in cutting, at least the portion being made of a high hardnessmaterial such as diamond, and also relates to a method for manufacturingthe cutting tool.

BACKGROUND ART

A cutting tool for precision cutting includes a portion involved incutting that is made of a material that has a high hardness and a highresistance to polishing, such as diamond.

As in the case of a general-purpose cutting tool, this cutting tool forprecision cutting also includes a rake face, a flank face, and a cuttingedge, formed of a ridge at a position at which these faces meet.

Since the portion involved in cutting is made of a material such asdiamond having a high hardness, operations such as cutting of thematerial or deepening of the rake face are performed by laser machiningduring manufacturing of this cutting tool for precision cutting.Manufacture of tools using a laser machine has been disclosed in, forexample, Patent Literatures (PTLs) 1 to 3.

CITATION LIST Patent Literature

PTL 1: JP 2003-25118 A

PTL 2: JP 2004-344957 A

PTL 3: JP 2008-229810 A

SUMMARY OF INVENTION Technical Problem

A surface formed on a high hardness material by being processed by alaser machine hardly ever has a smooth surface roughness. For thisreason, the cutting tool having a rake face or a flank face processed bylaser beams does not operate stably. As a countermeasure to address thisproblem, the surface of the tool, particularly the rake face, has beensubjected to machine polishing or grinding to increase the surfacesmoothness. However, since the material to be processed is hard, theexisting method of polishing the entire rake face is disadvantageous inthat it takes a long time for polishing or grinding.

This polishing or grinding causes a load on an polisher or a grinder,resulting in another problem of a cost increase.

To address this, the present invention aims to stabilize the cuttingperformance of a cutting tool for precision cutting by reducing the areasubjected to polishing or grinding during manufacturing of the tool.

Solution to Problem

In order to solve the above-described problems, the present inventionprovides a cutting tool including a portion made of a high hardnessmaterial in the following manner.

Specifically, the portion includes a rake face, a flank face, and acutting edge, formed of a ridge at a position at which the rake face andthe flank face meet, and the rake face is divided into a region A alongthe cutting edge and a region B excluding the region A of the rake face,a surface roughness of the region A is smaller than a surface roughnessof the region B, and the region B is deepened with respect to a positionof the region A.

In this structure, the region A of the rake face can be a surfacesmoothed by machining (polished or ground surface) and the region B isan unsmoothed surface processed using laser beams.

The present invention is also applicable to a cutting tool in which asintered cubic boron nitride (CBN) compact is used as the high hardnessmaterial. When the present invention is applied to a cutting tool inwhich diamond is used, which is so hard that roughing of the rake faceis inevitably dependent on laser machining, the effects of the presentinvention are particularly significantly exerted.

Diamond used for the cutting tool of the present invention may be anyone of monocrystalline diamond, sintered diamond, and polycrystallinediamond manufactured by a vapor deposition formation method. In thecutting tool of the present invention, the region A of the rake face ispreferably composed of a single surface.

The cutting tool can be manufactured by the following method in which,firstly, the rake face is processed on the high hardness material by alaser machine, and in the laser machining step, the region B of the rakeface is deepened so as to be deeper than the region A and then theregion A of the rake face is smoothed by machine polishing or grindingto form a cutting edge between the rake face and the flank face. Thepresent invention also provides this manufacturing method.

The effects of the present invention can be obtained also when part ofthe region B is subjected to deepening by this method.

It is preferable in this method that the flank face be also polished orground. The polishing or grinding of the flank face may be performedeither before or after the smoothing of the rake face.

Advantageous Effects of Invention

In the cutting tool according to the present invention, the rake face isdivided into a region A along the cutting edge and a region B excludingthe region A of the rake face, and the region B is deepened with respectto the position of the region A. Thus, the cutting toll can bemanufactured by a method of processing the regions A and B of the rakeface using a laser machine and then smoothing the region A by machinepolishing or grinding.

This method can minimize the area of the region A to be smoothed andsignificantly reduce the time for polishing and grinding.

Moreover, reduction of the area of the region A to be smoothed reduces aload on a polisher or a grinder during processing and thus reduces aprocessing cost.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view illustrating an example of a cutting tool(ball end mill) according to the present invention.

FIG. 2 is a perspective view of a main portion of the cutting toolillustrated in FIG. 1 in an enlarged manner.

FIG. 3 is a cross-sectional view of a portion illustrated in FIG. 2taken along the line III-III in an enlarged manner.

FIG. 4( a) illustrates a procedure of processing a rake face by amanufacturing method according to the present invention.

FIG. 4( b) illustrates a procedure of processing a rake face by themanufacturing method according to the present invention.

FIG. 4( c) illustrates a procedure of processing a rake face by themanufacturing method according to the present invention.

DESCRIPTION OF EMBODIMENTS

Referring now to FIGS. 1 to 4( c), a cutting tool according to anembodiment of the present invention is described below.

FIGS. 1 and 2 illustrate an example in which the present invention isapplied to a single-flute ball end mill having a radius at the end of0.5 mm (diameter of 1 mm). A cutting tool (ball end mill) 1 thusillustrated includes a main portion 2, which includes a shank 2 a, and acutting head 3 connected to the end of the main portion 2 and made of ahigh hardness material. The cutting head 3 includes a rake face 4, aflank face 5, and a cutting edge 6, formed of a ridge at a position atwhich the rake face and the flank face meet.

The reference numeral 7 in the drawings denotes a removal surface beyondwhich a portion of the cutting head 3 that does not include the cuttingedge 6 is removed.

The main portion 2 is made of tool steel such as high-speed steel orcemented carbide. The cutting head 3 is made of, for example, abinderless sintered diamond compact in which nanosized polycrystallinediamond is coupled without using a binder.

The rake face 4 formed in the cutting head 3 is divided into two regionsincluding a region A, which is located along the cutting edge 6, and aregion B, which is a region excluding the region A. The region B isslightly deepened with respect to a position of the region A and thesurface roughness of the region B is larger than the surface roughnessof the region A.

The region A is a surface subjected to machining, while the region B isa surface subjected to laser beam processing. The rake face 4 includingthese regions A and B is formed by being subjected to the followingsteps.

Specifically, the entirety of the rake face 4 is firstly processed by alaser machine, as illustrated in FIG. 4( a). This processing may beperformed by irradiating the rake face 4 with laser beams in thedirection in which the laser beams intersect the rake face 4 or in thedirection in which the laser beams are parallel to the rake face 4.

Subsequently, a portion of the rake face 4 excluding the region A (thatis, the region B) is further deepened by the laser machine. Theillustrated cutting tool (ball end mill) is deepened by irradiating theregion B of the rake face 4 with laser beams from immediately above theregion B.

Here, if the laser beams are caused to pass over the region B so as toleave a semicircular processed portion as illustrated in FIG. 4( b), thewidth of the region A can be made uniform.

When the entirety of the region B is subjected to deepening, the effectof reduction of the area of the rake face to be processed is maximized.The area of the rake face to be ground can be also reduced by leaving amountain having a peak at the same level as the region A between groovesproduced by causing the laser beams to pass over the area, although thereduction is smaller than that in the case where the entire surface issubjected to deepening.

FIG. 4( c) illustrates the state in which the entire region B has beendeepened while moving the position over which the laser beam is causedto pass in the radial direction of the end mill.

Here, the depth of the region B from the region A (the height H from thedeepest point of the region B to the region A illustrated in FIG. 3) ispreferably 100 μm or smaller so that wasteful deepening with laser beamcan be avoided. The lowest limit of the depth may even be 1 μm. Thewidth W of the region A illustrated in FIG. 4( c) is preferably 50% thediameter of the cutting edge 6 or smaller. In precision cutting, thedepth of cut is typically set at a fine value smaller than or equal to10 μm and thus a large value is not required for the width W. In termsof reduction of the area of the region A, a smaller width is better andthe lower limit may be 1 μm.

When the deepening of the region B is completed, the region A is thenfinished by machine polishing or grinding. Since the region A has asmall area and makes up a significantly small proportion of the entirerake face 4, time and labor taken for the machine polishing or grindingis significantly reduced.

The flank face 5 and the removal surface 7 are processed by the lasermachine. The flank face 5 is finished by polishing or grinding before orafter the region A of the rake face 4 is smoothed.

The flank face 5 may be processed only by the laser machine. However, asdescribed above, if the region A of the rake face 4 and the flank face 5are both subjected to polishing or grinding, a high-precision stablecutting edge can be obtained.

Objects to which the present invention is applicable are not limited tothe illustrated ball end mill. The present invention is applicable toother end mills such as a square end mill or a radius end mill. Thepresent invention is also applicable to cutting tools other than endmills, a precision turning tool, a cutting insert for tool, or boringtools such as a drill.

The cutting tool illustrated as an example includes a cutting head 3,the entire of which is made of a high hardness material. Instead, a highhardness material may be connected to a portion of the cutting head 3and only a portion involved in cutting (a portion near the cutting edge)may be made of the high hardness material.

Alternatively, a high hardness material which a portion involved incutting is made of may be monocrystalline diamond, sintered diamond, orpolycrystalline diamond manufactured by a vapor deposition formationmethod. Also in the case where a sintered cubic boron nitride (CBN)compact is used, the effects of the present invention can be expected,although the effects are smaller than those in the case where diamond isused.

Reference Signs List

-   1 cutting tool-   2 main portion-   2 a shank-   3 cutting head-   4 rake face-   A region along cutting edge of rake face-   B region excluding region A of rake face-   5 flank face-   6 cutting edge-   7 removal surface

1-5. (canceled)
 6. A cutting tool comprising a portion made of a highhardness material, wherein the portion includes a rake face, a flankface, and a cutting edge, formed of a ridge at a position at which therake face and the flank face meet, and wherein the rake face is dividedinto a region A along the cutting edge and a region B excluding theregion A of the rake face, a surface roughness of the region A issmaller than a surface roughness of the region B, and the region B isdeepened with respect to a position of the region A.
 7. The cutting toolaccording to claim 6, wherein the region A of the rake face is a surfacesmoothed by machine polishing or grinding and the region B is anunsmoothed surface subjected to laser machining
 8. The cutting toolaccording to claim 6, wherein the high hardness material is any one ofmonocrystalline diamond, sintered diamond, and polycrystalline diamond.9. The cutting tool according to claim 6, wherein the region A of therake face is composed of a single surface.
 10. A method formanufacturing the cutting tool according to claim 6, comprising a lasermachining step of forming the rake face on the high hardness materialusing a laser beam, wherein in the laser machining step, the region B ofthe rake face is deepened so as to be deeper than the region A and thenthe region A of the rake face is polished or ground to form a cuttingedge between the rake face and the flank face.